1. Field of the Invention
The present invention relates to an ink jet recording method and an ink jet recorder. In particular, the invention relates to the ink jet recording method and an ink jet recorder for recording at a substantially constant density regardless of record resolution and temperature.
2. Description of the Related Art
Today, conventional impact recorders are being replaced by non-impact recorders, for which the market is greatly growing. Of all non-impact recorders, ink jet recorders have the simplest principle. In addition, ink jet recorders provide easy multiple gradation and easy color recording. Among others, drop-on-demand type ink jet recorders, which eject only ink droplets for recording, have been rapidly widespread because of their high ejection efficiency and low running cost.
The viscosity of ink decreases as temperature rises. Accordingly, if the record head of an ink jet recorder of this type was driven at a constant voltage for any temperature, the droplet ejection speed and droplet volume would increase at a higher temperature, increasing the record density. Therefore, common ink jet recorders of this type are each fitted with a temperature sensor for detecting the temperature of the ink in the record head or the temperature around the head. As shown in FIG. 5 of the accompanying drawings, the drive voltage is lowered as the temperature rises. This controls the record density in such a manner that it does not vary with the temperature.
In recent years, in order to print image data such as photograph with higher reproducibility, it has been demanded that the volume of ink droplets be smaller and the record resolution be higher. Accordingly, the resolution has commonly been selected depending on the purpose. Specifically, low resolution (for example, 300xc3x97300 dpi) has been selected for high-speed recording, while high resolution (for example, 600xc3x97600 dpi) has been selected for high-quality recording.
The required volume of ink droplets depends on the resolution. For example, about 60 pl (picoliters) and about 15 pl are needed for 300xc3x97300 dpi and 600xc3x97600 dpi, respectively. The droplet volume is controlled by changing the drive waveform and/or drive voltage.
For conventional ink ejectors of this type, the drive voltage curve shown in FIG. 5, which represents the relationship between temperature and drive voltage, was used for any resolution. However, many recording tests have revealed that, if there is difference in record resolution among different cases, where the ejected ink droplets differ in volume, the relationships between temperature and record density are not completely the same. Specifically, the tests have revealed that, if the ink droplets are smaller, the density change with temperature is slighter. FIG. 6 shows two conventional cases where ink droplets different in volume were ejected for different resolutions. In FIG. 6, the solid thick line represents the case where the larger droplets for the lower resolution were ejected along a drive voltage curve for constant density at any temperature. In FIG. 6, the dotted line represents the case where the smaller droplets for the higher resolution were ejected along the same voltage curve. It has been revealed as shown in FIG. 6 that, in the latter case, the density is higher at lower temperatures and it is lower at higher temperatures. There may therefore be a case where the density does not change with temperature for low-resolution recording, but it does for high-resolution recording.
It is the object of the present invention to provide an ink jet recording method and an ink jet recorder for recording at a constant record density for any record resolution and any temperature.
In accordance with a first aspect of the present invention, an ink jet recording method is provided for recording on a record medium by means of a recorder including an actuator, which has an ink channel filled with ink and a nozzle communicating with the channel. A drive voltage can be applied to the actuator so that the ink channel changes in volume to eject ink therefrom through the nozzle. This recording method comprises the steps of:
detecting the temperature of the ink or the ambient temperature around the ink;
controlling the drive voltage depending on the detected temperature and record resolution; and
driving the actuator at the controlled voltage to eject ink from the ink channel through the nozzle.
The drive voltage may be lowered as the detected temperature rises. A rate of change in the drive voltage with respect to the temperature may change. The rate of change may be smaller for higher record resolution. This makes the record density roughly constant for any record resolution at any temperature, making it possible to do recording with constant quality.
The rate of change in drive voltage respect to with temperature may be determined for substantially constant record density within a predetermined temperature range, which may range between 5xc2x0 C. and 45xc2x0 C.
The recording method may include the step of selecting a pulse waveform for application to the actuator depending on the record resolution. This makes it possible to eject the volume of ink necessary for the record resolution. The amplitude of the pulse waveform may be lowered as the detected temperature rises.
For higher record resolution, fewer ink droplets may be ejected to form a dot on the record medium.
In accordance with a second aspect of the present invention, an ink jet recorder is provided. The recorder includes an actuator having an ink channel which can be filled with ink and a nozzle communicating with the channel. The ink channel can change in volume to eject ink from it through the nozzle when a drive voltage is applied to the actuator. The recorder also includes a switch for selecting a record resolution. The recorder also includes a temperature detector for detecting the temperature of the ink or the ambient temperature around the ink. The recorder also includes a controller for controlling the drive voltage depending on the selected resolution and the detected temperature. The controller may lower the drive voltage as the detected temperature rises. A rate of change in the drive voltage may change with respect to the ink temperature or the ambient temperature. The controller may reduce the rate of change as the selected resolution rises. The controller may make an absolute value of the rate of change in the drive voltage 0.8 or less if the selected resolution is four times (xc3x974) or higher per unit area with respect to a standard resolution, for example, the resolution is increased from 300 dpixc3x97300 dpi to 600 dpi xc3x97600 dpi. This makes the record density roughly constant at any temperature, making it possible to do recording with constant quality.
The controller may determine the absolute value of the rate of change so that the record density is substantially constant within a predetermined temperature range. The predetermined temperature may range between 5xc2x0 C. and 45xc2x0 C.
The controller may select a pulse waveform for application to the actuator depending on the selected resolution. The controller may lower the amplitude of the pulse waveform as the detected temperature rises. For higher record resolution, fewer ink droplets may be ejected from the nozzle to form a dot on a record medium. The recorder may further include a driver for driving the actuator. The controller may send a control signal to the driver. The record resolution may be selected from at least 300xc3x97300 dpi and 600 xc3x97600 dpi.